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1. 07:02 PM - Re: Jabiru 3300 voltage regulator (Robert L. Nuckolls, III)
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| Subject: | Re: Jabiru 3300 voltage regulator |
At 12:43 PM 8/24/2018, you wrote:
>I am helping a friend install a Jabiru 2200 on an Excalibur light
>sport airplane that has a much simpler electrical system than you
>are building. I checked the Jabiru manual and found that they are
>using a permanent magnet alternator with single phase AC
>output. The regulator that Jabiru supplied with the engine is the
>type that puts a full load on the alternator at all times then
>rectifies the output and regulates it down to 14 volts.
This 'shunt regulation' philosophy for small engine
PM alternators was indeed popular and practical when
mini-bike builders wanted to add batteries and headlights
to their products. Total system energy requirements were on the
order of 10 watts or less . . . not unlike that produced
by those little generators we used to put on our bicycles.
The had to be designed to tolerate continuous short
circuit loading. I.e. wound with smaller, high resistance
wire and well heat-sinked to dissipate the energy developed
when a battery became fully charged and the shunting device,
usually an SCR, was triggering early in every half cycle of
the dynamo's output. Simple and sorta worked purddy gud . . .
Emacs!
Then came snowmobiles, ski-doos, etc, etc and the batteries
got bigger, lights more powerful, starters were added, etc.
etc. But the common vernacular for the ac dynamo on the engine
was a 'lighting coil'.
But as the system energy requirements went up, output
demands from the dynamo and its companion regulator did
too. A fundamental concern for any solid state power management
is what to do with and about wasted heat. You can do it
with a combination of two techniques: (1) reduce the heat
dissipated in the circuit components and (2) add heat sinking
which may included fins to dissipate energy into convection
or forced air.
(1) is where you start from.
Emacs!
The legacy, gated full wave rectifier shown above is
typical of most if not ALL rectifier regulators of 20
or so years ago. Some people have mistakenly called this
a 'shunt' regulator because of the totem-pole of rectifier-
SCR strings across the alternator winding. It may LOOK
like some kind of 'shunt' circuit but in fact, those
four devices in the bridge are only turned ON in pairs
and in series connection with the alternator winding.
The 'transistors' you see above are in fact 4-layer,
triacs or scrs. They are the major heat dissipating
devices in the circuit. Some manufacturer's have
eliminated the 4-layer devices in favor of MOSFET
transistors which typically have perhaps 5% of the
dissipation of the SCR. These modern R/R's run much
cooler and are more efficient.
Once you've refined your circuit components, you then
PACKAGE the thing to manage heat that 20A+ components
invariably throw off.
But these are still gated, SERIES, full wave bridge rectifiers.
Nobody would build a true SHUNT style regulator reminiscent
of your daddy's moped. It's inefficient, wasteful, difficult
to manage thermally and best yet . . . completely unnecessary.
If someone claims to HAVE a shunt style rectifier/regulator,
ask them to put a snap-on ammeter on one of the alternator
leads while system loads are minimized and the battery is
charged.
If it's a shunt style regulator, current flowing in that
loop with minimized alternator loads would be high. I'll
offer to give $100 to anyone who can send me a SHUNT
style R/R rated at 10A or more to test on my stand along
with identification of where it came from and on what
vehicle it is used. I'll test here, write a report and
return the R/R to the owner with or without the $100
as dictated by test results.
I'll bet the Jabiru 3300 R/R is no different electronically
than the Ducatti regulators supplied with Rotax engines all
these years.
Bob . . .
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